For preparing a TFT-LCD (Thin Film Transistor Liquid Crystal Display), it is required to form a through-hole for electrical connection in a film layer above a substrate, and then form an ITO (Indium Tin Oxide) layer on the through-hole. In a process of forming the ITO layer, dirt and impurities are prone to enter the through-hole. In addition, the ITO layer has poor compactness and water vapor is easy to pass through the ITO layer to be in direct contact with a metal such as Mo, AL and Nd in a gate layer or a source-drain layer below the ITO layer, which will lead to electrochemical corrosion, and damage performance of the film layer and reduce product yield.